1. Technical Field
Embodiments of the subject matter disclosed herein generally relate to apparatuses configured to provide a visual indication outside a blowout preventer (BOP), relative to a current position of ram blocks inside the BOP, and methods of adding such apparatuses to new or existing blowout preventers.
2. Discussion of the Background
Oil and gas extraction remains a critical component of the world economy in spite of increasing challenges regarding the accessibility and the safety of oil and gas exploitation. The drilling at offshore locations to extract oil and gas from under the sea floor is performed at ever increasing water depths.
A traditional offshore oil and gas installation 10, as illustrated in FIG. 1, includes a platform 20 (of any other type of vessel at the water surface) connected via a riser 30 to a wellhead 40 on the seabed 50. It is noted that the elements shown in FIG. 1 are not drawn to scale and no dimensions should be inferred from relative sizes and distances illustrated in FIG. 1.
A subsea blowout preventer stack (BOP) 60 is located close to the seabed 50, and may include a lower BOP stack 62 attached to the wellhead 40, and a Lower Marine Riser Package (“LMRP”) 64, which is attached to a distal end of the riser 30. During regular operation the lower BOP stack 62 and the LMRP 64 are connected. BOPs 66 located in the lower BOP stack 62 or in the LMRP 64 are in an open state during normal operation, but may be closed (i.e., switched in a close state) to interrupt a fluid flow through the riser 30. Electrical cables and/or hydraulic lines 70 transport control signals from the drilling platform 20 to a controller 80, which is disposed on the BOP stack 60. The controller 80 controls the BOPs 66 to be in the open state or in the close state, according to signals received from the platform 20 via the electrical cables and/or hydraulic lines 70. The controller 80 also acquires and sends to the platform 20, information related to the current state (open or closed) of the BOPs.
During drilling, gas, oil or other well fluids at a high pressure may burst from the drilled formations into riser. When such an event (which is sometimes referred to as a “kick” or a “blowout”) occurs at unpredictable moments, if the burst is not promptly controlled, the well and/or the equipment of the installation may be damaged. The BOPs are installed to seal the well when a blowout event occurs. Although the above discussion was directed to a subsea well, the same is true for wells on the ground.
A conventional BOP, as illustrated in FIG. 2, is essentially a valve configured to stop high pressure fluid flowing from the well into the riser 30. The BOP 100 in FIG. 2 (which can be any of the BOPs 66 in the subsea BOP stack 60) has a body 110 inside which two substantially perpendicular chambers 120 and 130 intersect. The first chamber 120 (vertical bore) connects to and is aligned with the riser 30.
The second chamber 130 houses two ram blocks 140 that are configured to move along an x-axis, which is perpendicular to the riser 30, the ram blocks 140 being pushed by respective piston rods 150 towards each other. Tail ends 160 of the piston rods 150 are respectively hosted inside end caps 170 of the body 110. This type of BOP (which has ram blocks) is known as a ram BOP.
During regular operation, the BOP 100 is in an open state, the ram blocks 140 being located at respective open positions, outside a space where the first chamber 120 intersects with the second chamber 130. When a kick event occurs, upon receiving a command from the controller 80, the ram blocks 140 move towards each other to close positions at which the ram blocks 140 are in contact, face-to-face with each other, inside the second chamber 130. When the ram blocks 140 reach the close positions the fluid flow passing therethrough is severed. The BOP 100 is then in a close state.
The controller 80 reports the state of the BOP 100 to the platform 20 by sending signals along the cables 70. However, when accidents occur, the cables 70 may become interrupted or the controller 80 may be damaged, and, therefore, it may become unknown by operators on the platform 20, whether a BOP had received the control signal and switched to a close state, or remained in an open state. Information about the state of the BOPs may be critical for preventing spills or for containing the spills of fluid bursting from the wellhead 40. Conventionally, this information cannot be retrieved if the normal information path is interrupted (e.g., if the cables 70 and/or the controller 80 are damaged).
Accordingly, it would be desirable to equip the BOPs with apparatuses providing visual indications outside the BOP relative to the current position of the ram blocks inside the BOPs, to be able to determine the state of the BOP by performing a visual inspection outside the BOP, for example, using a remote operational vehicle (ROV) equipped with an underwater video camera.
It would also be desirable to modify the conventional BOPs to include such visual indicators, thereby avoiding a situation in which the state of the BOP is not known and cannot be determined. Moreover, it would be desirable that such indicators to be independent of any source of power so that they will provide the information about the ram blocks even if such a source of power may become unavailable.